The preparation of gel polymer electrolytes using atom-transfer radical polymerization (ATRP) has been investigated. A liquid electrolyte with poly (ethylene glycol) methyl ether methacrylate and poly(ethylene glycol) dimethacrylate was successfully polymerized by ATRP at ambient temperature to form a gel polymer electrolyte. Infrared spectroscopy confirms that the polymerization of gel polymer electrolytes can take place at room temperature. The concentration of salt and the percentage of either polymer in electrolytes directly influence the ionic conductivity. An optimal ionic conductivity of the gel polymer electrolyte is obtained to be 2.1 x 10(-3) S cm(-1) at 30 degrees C. Furthermore, the lithium transference number is found to be about 0.32. Cyclic voltammogram and cell performance show that the gel polymer electrolyte has good electrochemical stability and good cyclability. (c) 2007 The Electrochemical Society.